A Flight Instructor maneuvering in a VFR practice area reported a NMAC with another aircraft that turned into their path.

Narrative

Performing slow flight while getting setup for approach into SDL. I (instructor onboard) noticed traffic (Aircraft Y) departing 25R from DVT low and right of my position. I maneuvered to give the traffic separation as they had right of way. Aircraft Y then turned into the direction of my plane. This happened 3 more times until I had to take extreme evasive maneuvers to avoid a midair collision (55 degrees bank left; 10 degrees nose low)I was monitoring the local practice area frequency and Aircraft Y was not on frequency for the local practice area; the respective Phoenix approach frequency OR with DVT Tower.I think it would benefit if there was a type of special air traffic rules area for high density VFR training areas such as phoenix. I notice MANY potential losses of separation occurring and the only reason they do not collide is from ADSB IN and instructors on board communicating. The GA population not involved with training isn't always aware of these frequencies used for the practice areas and it is a safety hazard especially when they do not have ADSB IN.